Temperature control system of gas-fired water heater

ABSTRACT

A temperature control system of a gas-fired water heater includes a cold water pipe connected to one side of a heat exchanger and a hot water pipe connected to another side of the heat exchanger. A circulation pump is mounted to a water return pipe, which has two ends respectively connected to the hot water pipe and the heat exchanger to direct and return hot water from the hot water pipe back to the heat exchanger. When a hot water faucet is opened to activate a combustion operation of the gas-fired water heater, the circulation pump is set in continuous operation to pump water from the water return pipe for returning back to the heat exchanger, so that the returned hot water can be mixed, in the heat exchanger, with cold water supplied through the cold water pipe in order to achieve a set temperature.

(a) TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a temperature control system, and more particularly to a temperature control system of a gas-fired water heater that involves a circulation pump for continuously pumping return water through a return water pipe into a heat exchanger.

(b) DESCRIPTION OF THE PRIOR ART

Referring to FIG. 3, a known tankless or hybrid water heater (involving a fire-tube heat exchanger) comprises, structurally, a cold water pipe 91 and a hot water pipe 92 arranged and connected to two sides of a heat exchanger 90 with a mixing valve 93 connected between the cold water pipe 91 and the hot water pipe 92 and an adjustment valve 94 mounted to the cold water pipe 91 in order to achieve a desired set temperature of hot water. An internal temperature of the known heat exchanger 90 is generally set at a level higher than the desired set temperature of hot water. (For example, the hot water set temperature is 50° C., and the temperature of the heat exchanger 90 is set at 70° C.) The mixing valve 93 (such as a stepping motor controlled valve) conducts hot water that is fed to the hot water pipe 92 by the heat exchanger 90 to mix with the cold water supplied through the cold water pipe 91 in order to achieve the precise set level of temperature.

Referring to FIG. 4, some of the known water heaters are provided with a pump 95, and a 2-way valve 96 is provided for temperature control. The purpose of the pump 95 is to eliminate or remove latent heat that is generated after the combustion operation of the heat exchanger 90 is shut down (namely the hot water faucet is closed).

The known water heaters suffer at least the following drawbacks:

(1) The heat exchanger 90 has to bear a relatively high thermal stress because a great temperature difference exists between a water inlet port (connected with the cold water pipe 91) and the water outlet port (connected to the hot water pipe 92) of the heat exchanger 90.

(2) Because of thermal inertia and thermal impact, the service life of the heat exchanger 90 is shortened.

(3) Due to latent heat of the heat exchanger 90, there are severe issues of excessively high and low temperatures.

(4) Loading applied to the mixing valve 93 and the 2-way valve 96 is heavy for they have to constantly adjust to accommodate different flow rates.

Thus, it is necessary for improvement of the known temperature control mechanism of water heaters.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a temperature control system of a gas-fired water heater that involves a circulation pump for continuously pumping water to return through a return water pipe back into a heat exchanger in order to constantly keep the temperature of the heat exchangers the same as a set temperature.

To achieve the above objective, the present invention comprises a heat exchanger, a cold water pipe, a hot water pipe, and a circulation pump, wherein the heat exchanger heats and converts cold water into hot water. The cold water pipe is connected to one side of the heat exchanger to supply cold water into the heat exchanger. The hot water pipe is connected to another side of the heat exchanger to output hot water generated by the heat exchanger. The circulation pump is mounted to a water return pipe. The water return pipe has two ends that are respectively connected to the hot water pipe and the heat exchanger to direct and return hot water from the hot water pipe back into the heat exchanger.

The present invention is provided with a circulation pump that takes the place of the traditionally used mixing valve and adjustment valve. When a hot water faucet is opened to activate a combustion operation of the gas-fired water heater, the circulation pump is constantly kept in operation to pump and return the hot water from the hot water pipe through the water return pipe, as returned water, back into the heat exchanger. At the same time, the cold water pipe supplies cold water into the heat exchanger so that the returned hot water and the cold water are mixed in the heat exchanger for preheating for the purpose of reaching a set temperature and making temperature control stable, without excessively high or excessively low temperature. The temperature of the heat exchanger can be always kept at the same level as the set temperature. The heat exchanger does not cause any issue of latent heat.

When the hot water faucet is closed to thus shut down the combustion operation of the gas-fired water heater, the circulation pump 40 is periodically set into operation at a fixed or variable interval in order to generate a water flow that helps reduce generation and accumulation of scale.

The foregoing objectives and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts.

Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the present invention.

FIG. 2 is a piping diagram of the present invention.

FIG. 3 is a block diagram illustrating of temperature control applied to a known tankless water heater.

FIG. 4 is a block diagram illustrating of temperature control applied to a known hybrid water heater.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims.

Referring to FIGS. 1 and 2, a temperature control system of a gas-fired water heater according to a preferred embodiment of the present invention comprises a heat exchanger 10, a cold water pipe 20, a hot water pipe 30, and a circulation pump 40. Details will be provided below:

The heat exchanger 10 is operable to heat and convert cold water into hot water with an operation principle that is commonly known and will be not repeated herein.

The cold water pipe 20 is connected to one side of the heat exchanger 10 to supply cold water to the heat exchanger 10.

The hot water pipe 30 is connected to another side of the heat exchanger 10 to output hot water generated by the heat exchanger 10.

The circulation pump 40 is mounted to a water return pipe 50. The water return pipe 50 has two ends respectively connected to the hot water pipe 30 and the heat exchanger 10 to direct hot water from the hot water pipe 30 back to the heat exchanger 10.

In an embodiment, the heat exchanger 10 comprises a water tank. The water tank has a capacity that is less than or equal to 10 gallons, this covering heat exchangers of the instantaneous heating type (which has no water storage at all) or fire tube type and hybrid type (which have a minor amount of water storage). For water storage greater than such a range may not achieve a uniform temperature inside the tank and may not be capable of effective control of temperature.

In an embodiment, the water return pipe 50 is connected to the hot water pipe 30 and the heat exchanger 10 to form an internal circulation. The connection between the water return pipe 50 and the heat exchanger 10 forms an inlet port of return water, which is not set at the same location as that of an inlet port of cold water formed of the connection between the cold water pipe 20 and the heat exchanger 10.

In an embodiment, the heat exchanger 10 is combined with a combustion blower 60, wherein the combustion blower 60 is connected to a fuel gas pipe 61 and the fuel gas pipe 61 comprises a fuel gas valve 62, for supplying fuel gas to the heat exchanger 10 to serve as a combustion heat source.

The above provides a description to the components of the present invention and the assembly thereof. Examples of use, features, and advantages of the present invention will be illustrated below.

The present invention is applied to a circulation pump 40 to take the place of the traditionally used mixing value and adjustment valve. When a hot water faucet is opened to cause activation of a gas-fired water heater for combustion, the circulation pump 40 is constantly supplied with electrical power to continuously drive hot water from the hot water pipe 30, through the water return pipe 50, back into the heat exchanger 10 so as to achieve continuous circulation of the return water, and at the same time, the cold water pipe supplies cold water into the heat exchanger, so that the cold water is mixed with the return water in the heat exchanger 10 for pre-heating to reach a set temperature (for example a temperature of hot water being set at 50° C.). Temperature control in this way is stable so that no excessively high or excessively low temperature may occur. The temperature of the heat exchanger 10 can be constantly kept at the set temperature and no latent heat may occur in the heat exchanger 10.

When the hot water faucet is closed to have the combustion operation of the gas-fired water heater shut down, the circulation pump 40 is periodically set into operation at a fixed or variable interval so that flowing water helps reduce accumulation and generation of scale.

The present invention possesses at least the following advantages:

(1) The temperature of the heat exchanger 10 is constantly kept the same as the set temperature.

(2) The heat exchanger 10 has no temperature hysteresis.

(3) The heat exchanger 10 has no latent heat so that the temperature at a hot water outlet is steady without excessively high or excessively low temperature thereby helping prevent burning caused by the latent heat of the heat exchanger 10.

(4) The circulation pump 40 is kept in operation during a water heating operation and is set into operation periodically at a fixed or variable interval in a standby period of the heater. As such, the flowing water, when moving in the heat exchanger 10, causes a water flow that helps reduce generation and accumulation of scale.

(5) The heat exchanger 10 has low thermal inertial and low thermal impact so that the service life can be extended.

(6) No mixing valve and adjustment valve are required so that the number of components can be reduced.

The following table provides a comparison of difference between the present invention and the conventional water heaters shown in FIGS. 3 and 4:

The Present Invention Prior Art Water Heaters purpose of to eliminate latent heat to provide internal or external pump circulation mode (only one mode being available) principle (1) the hot water activated (1) for internal mode, the of and combusting and the pump being set into operation operation pump kept in operation only after combustion is shut (2) shutting down combustion down in order to remove of the water heater, while the latent heat pump set in periodic (2) for external mode, the operation pump being arranged to (3) the pump being used only replace a circulation pump for internal circulation installed in a hot water (4) the temperature of the heat circulation pipe set up inside exchanger being equal to the a house in order to provide an set temperature external circulation of hot water (3) the temperature of the heat exchanger is always slightly higher than the set temperature and would be mixed with cold water from a bypass pipe (with a mixing valve) to reach the set temperature purpose of to balance the temperature of not suitable for temperature pump the heat exchanger in order to control (for the mixing valve instal- control temperature is the key component for lation temperature control) water which is a component other which the same part as the circulation than or not a part of a cold cold water pipe and return water pipe com- ponent purpose of to provide two different (1) return water being not water temperature zones: used to control temperature return (1) condensation efficiency of (2) after combustion is shut com- flue gas is made higher and down, the pump being ponent the result of flue gas allowed to operate for few condensation is better, heating seconds because the top of efficiency being higher the heat exchanger is (2) pre-heating of cold water excessively hot and the return supplied into the heat water is used to remove a part exchanger in order to control of the latent heat of the heat the water tank temperature of exchanger (this being the heat exchanger workable for only the internal (3) completely eliminating circulation mode) latent heat, achieving temperature control, free of thermal stress, achieving extended life span (4) reducing the number of components

It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above.

While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the claims of the present invention. 

I claim:
 1. A temperature control system of a gas-fired water heater, comprising: a heat exchanger, which heats and converts cold water into hot water; a cold water pipe, which is connected to one side of the heat exchanger to supply cold water to the heat exchanger; a hot water pipe, which is connected to another side of the heat exchange to output hot water generated by the heat exchanger; a circulation pump, which is mounted to a water return pipe, the water return pipe having two ends respectively connected to the hot water pipe and the heat exchanger to direct and return hot water contained in the hot water pipe back to the heat exchanger.
 2. The temperature control system of the gas-fired water heater according to claim 1, wherein the heat exchanger comprises a water tank, which has a capacity that is less than or equal to 10 gallons.
 3. The temperature control system of the gas-fired water heater according to claim 1, wherein the water return pipe is connected to the hot water pipe and the heat exchanger to form an internal circulation such that the connection between the water return pipe and the heat exchanger forms an inlet port of the returned water, which is not at the same location as an inlet port of cold water formed as the connection between the cold water pipe and the heat exchanger.
 4. The temperature control system of the gas-fired water heater according to claim 1, wherein the heat exchanger is coupled to a combustion blower, wherein the combustion blower is connected to a fuel gas pipe and the fuel gas pipe comprises a fuel gas valve for supplying fuel gas to the heat exchanger to serve as a combustion heat source to serve as a combustion heat source. 